The present invention concerns a cutting bit for camshaft milling cutters and a corresponding disc milling cutter for camshaft milling. Corresponding cutting bits are already known in the state of the art, which comprise a substantially cuboidal cutting body with an upper face and a lower face oriented substantially parallel to one another and which have side faces. Cutting edges are formed along the lines of intersection of side faces with the top side and/or the underside.
The cutting bits can be rectangular, preferably square in plan view. When mutually oppositely disposed side faces of such cutting bits extend substantially parallel to each other, that generally involves a negative rake angle, by virtue of the necessity for providing a relief surface behind the cutting edge. Cutting bits or cutting inserts of that kind are therefore also referred to for the sake of brevity as “negative cutting bits”.
If the upper face is smaller than the lower face or vice-versa, then a cutting edge involving positive cutting geometry can be provided at the transition of the side faces which are then correspondingly inclined, in relation to the respective larger one of the upper and lower faces. The cutting bits according to the present invention can be both positive and negative cutting bits or inserts.
Rectangular or preferably square cutting bits of that kind are particularly extensively used on milling cutter heads for milling crankshafts and camshafts. For that purpose, suitable cutting bits are arranged along the periphery of a cylindrical main portion of a disc milling cutter and such a disc milling cutter is then caused to rotate about its axis and is moved in a radial direction towards a crankshaft or camshaft which can possibly also be rotated about a longitudinal axis so that wide grooves are milled out of an initially relatively thick, solid metal shaft, in individual regions thereof, and the remaining parts thereof are profiled so that the overall result is the desired profile of a camshaft or also a crankshaft.
In that respect, particularly when dealing with camshafts, the situation very regularly sees the occurrence of a special profile shape which is provided between two spaced-apart grooves on a cam which can also be present in the form of an eccentrically displaced, cylindrical part. That profile is characterized by beveling or chamfering of the edges, wherein a cylindrical part of slightly smaller diameter again adjoins one of those chamfers.
Such a profile can be seen on the part of a camshaft as is illustrated in FIG. 1 at reference numeral 30 for two cylindrical, non-coaxial parts of a camshaft.
In this case, those parts do not necessarily have to be cylindrical but they can be of a cam contour which in principle can be any desired contour and which deviates from a circular shape which however is not visible in the view shown in FIG. 1.
The production of corresponding profiles is relatively complicated and expensive with the cutting bits and milling cutter heads known in the state of the art, and conventionally, to produce a profile corresponding to the profile of the cam 30 in FIG. 1, milling cutter heads with two displaced rows of cutting bits are used in order to produce the cylindrical part while two further rows of bits are used for producing the chamfers or bevels and the short cylindrical attachment portion. Therefore, if such profiles are to be produced in one pass, it is necessary to provide mounting devices for four different rows of cutting bits along the periphery of a disc milling cutter which is in the basic shape of a cylindrical disc. Unless various types of cutting inserts are also to be used for that purpose, such a disc milling cutter must have four different and in particular differently oriented rows of mounting pockets for suitable cutting bits. As moreover the cutting regions of such cutting bits must necessarily overlap in order to cover the entire profile, all those various cutting bit mountings have to be displaced relative to each other in the peripheral direction along the outside periphery of a disc milling cutter, which in turn means that the cutting bits which are to produce one and the same part of the profile must be at relatively large spacings relative to each other. That reduces the capacity and efficiency of corresponding milling cutters. Alternatively, it would be possible for the various parts of the profile to be produced in a plurality of working operations involving various milling cutter heads, which however is detrimental in terms of efficiency of production.
In comparison with that state of the art, the object of the present invention is to provide a cutting bit and a corresponding disc milling cutter which are simpler to produce and by virtue of the use of which, it is possible to produce cam profiles with a straight main part (for example cylindrical) which is parallel to the axis, bevels at the edges and/or at one or both sides extension portions of smaller diameter, at a higher level of efficiency.